1. Field of the Invention
The present invention relates to a sealing apparatus for sealing (or welding) two or more sheets, such as thermoplastic films, thermoplastic nonwoven fabrics or a combination thereof, and a sealing method using the sealing apparatus, more particularly, relates to a sealing apparatus suitable for use in manufacturing an article having a seal, such as disposable diaper or sanitary napkin, and a sealing method using the sealing apparatus.
2. Description of the Related Art
Sealing apparatuses which can seal a stack of two or more sheets such as thermoplastic resin films or nonwoven fabrics comprising thermoplastic fibers by fusing the films or fibers are disclosed, for example, in Japanese Unexamined Patent Publication No. H05-15551 (Patent Publication 1) and Japanese Examined Patent Publication No. H02-43631 (Patent Publication 2). As disclosed in the Patent Publication 1, such a sealing apparatus may be installed in a process for manufacturing a disposable diaper or the like.
In order to seal a band-shaped soft workpiece such as the stack of resin films or nonwoven fabrics to have seals at a constant pitch in a feed direction of the workpiece or a seal continuously extending in the feed direction of the workpiece, it is necessary to firmly support the soft workpiece with a proper tension being given thereto. In a conventional sealing apparatus, accordingly, the workpiece is fed onto a periphery of a rotary drum so that as the rotary drum is driven to rotate, the workpiece moves in the direction of rotation, as in the Patent Publications 1 and 2. The workpiece thus fed and wound about the peripheral surface of the rotary drum may be firmly supported by the periphery of the rotary drum with a proper tension being given thereto.
Furthermore, the apparatus has an anvil disposed on the peripheral surface of the rotary drum and an ultrasonic horn for facing the anvil. The workpiece moving along with the peripheral surface of the rotary drum may be held between the anvil and the ultrasonic horn so as to be fused and sealed due to heat internally generated by ultrasonic vibration applied from the ultrasonic horn.
In such a conventional soft workpiece sealing apparatus, however, the ultrasonic horn is fixed in a position facing the peripheral surface of the rotary drum, as in the Patent Publications 1 and 2. Then, when the workpiece moving along with the peripheral surface of the rotary drum is held between the anvil and the ultrasonic horn, the ultrasonic vibration is applied from the ultrasonic horn to the workpiece that is sliding on the ultrasonic horn.
Accordingly, since the ultrasonic vibration from the ultrasonic horn cannot be applied sufficiently long to areas of the workpiece to be sealed, sealing failure tends to occur in the workpiece. Such sealing failure due to a decrease in vibrational energy applied to the workpiece may occur more frequently as the rotating velocity of the rotary drum is increased to let the workpiece move at a higher velocity for sealing, which results in an extremely high relative velocity of the workpiece and the anvil against the ultrasonic horn.